The present invention refers to a device for actuating a membrane arranged in an opening to a space, wherein the membrane has a first surface and a second opposite surface, and is limited by an edge area extending around the membrane.
It is known to use such devices for actuating a membrane arranged to generate sound. The membrane may for instance generate sound in the form of music or any other desired sound. The membrane may also be arranged to generate sound for attenuating other sounds, so called active sound reduction. Different types of such membranes are known, for instance in various types of loudspeaker designs, various types of panels such as hat racks in vehicles or windowpanes in vehicles.
U.S. Pat. No. 4,551,849 discloses a sound reducing system arranged to vibrate a panel in a vehicle. In the first place, this document is directed to the vibration of the hat rack. Also other types of panels are mentioned, for instance side doors, instrument panels etc.
U.S. Pat. No. 5,812,684 discloses another device for active sound reducing in motor vehicles, in particular for reducing noise from outside. The device includes an actuating member in the form of a piezoceramic element which is arranged to vibrate a windowpane of the vehicle. The pane disclosed is supported by an elastomeric strip extending around the pane.
JP-A-06205497 discloses a device for vibrating a rear window of a vehicle in order to generate low frequency sound. The device includes an actuating member acting against the window at a substantially central point thereof. The window is supported in the vehicle in a conventional manner by means of a rubber strip.
WO96/35313 discloses a device for obtaining acoustic vibrations in a medium by means of a transparent body, for instance a windowpane. In an embodiment, a windowpane is brought to vibrate by means of a piezoelectric element that is connected to a frame and extends between the frame and the pane proper.
During certain conditions windowpanes are suitable for obtaining sound with a relatively low frequency. These windowpanes may thereby advantageously be used as bass loudspeakers included in a music equipment or sound-generating element in a device for reducing or attenuating sound or noise, i.e. in particular low frequency sound. Windowpanes often have a relatively large surface and are thanks to a curved or double curved design relatively rigid. As actuating members for vibrating a membrane or for instance a windowpane it is known to use piezoelements. One problem with such piezoelements is however that the length of stroke obtained is too short for bringing a windowpane to a movement with a sufficient amplitude in an efficient manner. An other important precondition for being able to vibrate such a membrane in an efficient manner is that the membrane is supported by a flexible device permitting the vibration of the membrane. It is then important that the parts of the actuating device, which are not actuating the pane, have a small resistance against the movement of the membrane.